Marshall B150 -56vdc on speaker output

[goldtop5]

I have a Marshall B150 bass combo amp that's got -56vdc on the speaker output. I'm trying to chase it down but still cannot find the fault. I replaced all the output transistors, but it still has the same problem. What are the possibilities? Thanks!

[g1]

Schematic is attached.
Were the output devices all blown? Did you check TR4?
Did you check all the associated resistors and diodes with the output devices and TR4?
Failure of any of these parts can put DC offset on the output.

[soundguruman]

are you measuring between amp chassis ground and tip of speaker cable?
The speaker output is not grounded to the chassis.
So, make sure you are measuring the two speaker wires only. There could be a mistake in the measurement...

[Enzo]

The return lead of the speaker is above ground by only 0.33 ohms, R37. If you measure DC on the output lead, that resistor is not going to skew the readings. If there is 56v on the output lead, it will be on the speaker too, and the speaker will not care at all that there is a 0.33 ohm resistor in series, it will still be a burnt up speaker.